NIKI BACCILE1*, CHLOÉ SEYRIG1, PAULINE CHAPUIS2, ABDELLAH YOUSFI2
*Corresponding author
1. Sorbonne Université, Centre National de la Recherche Scientifique, Laboratoire de Chimie de la Matière Condensée de Paris, Paris, France
2. AYCC Cosmetic Creation, Chatillon, France

Abstract

Sophorolipids (SL) are well-known biosurfactants produced by the yeast S. bombicola, generally in a complex mixture between its lactonic and open acidic forms, both being partially acetylated. To overcome this issue, by alkaline hydrolysis we generate a fully acidic, non-acetyalted, form of SL. This acidic SL has a pH-responsive behaviour and above pH 6 can form complex coacervates with high-molecular weight chitosan by a simple mechanism of electrostatic attraction between the negative and positive forms of SL and chitosan, respectively. SL-chitosan complex coacervates are able to stabilize O/W emulsions by a Pickering mechanism. We show here their application in the formulation of O/W emulsions containing cosmetics-relevant raw materials, oils, preservatives and vitamins.

INTRODUCTION
Microbial biosurfactants are broadly intended as amphiphilic molecules obtained by the fermentation process of sugars and vegetable oils by specific yeast and bacteria (Figure 1) (1, 2). Considering the more stringent regulations combined with the worldwide consumers’ concerns for health and environment, biosurfactants are the obvious eco-friendly option to develop potentially commercial alternatives to petrochemical surfactants, especially in the field of cosmetics,(3,4) a field of application which is quite old (5).

Among the most widely known biosurfactants, sophorolipids are one of the most attractive classes. They are produced from the yeast S. bombicola, with interesting production rates and high titers. (6) Despite their apparent complex mixture of congeners, they can be easily hydrolyzed into one main, non-acetylated C18:1 acidic, congener, with well-characterized physicochemical properties (Figure 1). Along the years, sophorolipids have been studied within the context of cosmetics, (7) antimicrobial agents (8) or soft materials (9). In this regard, sophorolipids are known to have surface-active properties and ...